Selective laccase-catalyzed dimerization of phenolic compounds derived from lignin: Towards original symmetrical bio-based (bis) aromatic monomers

• A selective enzymatic process of vanillin dimerization is described.
• The divanillin is easily recovered as a precipitate.
• The selective formation of dimers by CC coupling was extended to six ortho-methoxy-para-substituted phenols.

A laccase-catalyzed process was developed to prepare, selectively, in high yield, dimers of lignin-based phenolic compounds without any purification. The influence of experimental parameters such as laccase loading, nature of solvent and the presence of oxygen on the conversion of vanillin was investigated. After the dimerization, the product obtained as a precipitate is filtered off and the solution containing the enzyme can be re-used several times, which improves the process economics. A phenolic-substrate screening reveals that such process enables to dimerize regioselectively, six ortho-methoxy-para-substituted phenols (vanillin, 4-hydroxy-3-methoxybenzonitrile, acetovanillon, methyl vanillate, 2-methoxy-4-methylphenol, and eugenol) with yields ranging from 87% to 96% and one ortho-disubstituted phenol (2,6-dimethoxyphenol) with 80% yield.

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